The long term objectives of this research program are to understand the mechanisms by which the replication of herpes simplex virus type-1 (HSV-1) is initiated. Specific protein-protein interactions among the proteins engaged in this process are considered as targets for antiviral therapeutics. These studies should also provide insight into the mechanisms by which DNA replication is initiated from more complex eukaryotic chromosomal origins. HSV-1 is the prototype of the herpesviridae family of viruses. These viruses are known to cause a multi of disease in humans. HSV-1 in particular is extremely widespread in the population, and is associated with a number of symptoms that are a result of both primary and recurrent infections. The most prevalent conditions caused by infections with HSV-1 are oro-labial and genital skin lesions. However of much greater significance are encephalitis and blindness that are brought on by HSV-1 infections. Initiation of origin-specific DNA replication involves the targeted destabilization of particular chromosomal elements by a group of proteins that makes the DNA accessible to the DNA synthesis machinery, HSV-1 and single-stranded DNA binding protein (ICP8). The UL9 protein and ICP8 are known to form a tight complex that may function in origin recognition and unwinding. We hypothesize that the interaction between the UL9 protein and ICP8 is an essential part of the initiation process. Accordingly, we propose to further characterize the ICP8-UL9 protein complex. We will also determine the importance of this protein-protein interaction for origin- specific DNA replication. We further hypothesize that efficient activation of the origin of DNA replication involves the action of cellular proteins that assist the viral initiator proteins. Our approach is to identify such proteins by using biochemical and genetic complementation assays to detect specific protein-protein interactions between the viral initiator proteins and potential cellular factors. We propose to examine the importance of such cellular proteins by determining their role in activating the origin of DNA replication in vitro.